Process for the oxidation of olefinammonia mixtures to unsaturated nitriles



United States Patent PROCESS FOR THE OXIDATION OF OLEFIN- AMMONIAMIXTURES TO UNSATURATED NITRILES James L. Callahan, Cuyahoga County,Ohio, and Berthold Gertisser, Essex County, N.J., assignors to TheStandard Oil Company, Cleveland, Ohio, a corporation of Ohio N0 Drawing.Filed Jan. 11, 1965, Ser. No. 462,460 6 Claims. (Cl. 260-465.3)

This invention relates to the oxidation of olefinammonia mixtures tounsaturated nitriles, such as propylene-ammonia to acrylonitrile andisobutylene-ammonia to meth-acrylonitrile using oxidation catalystsystems consisting essentially of oxides of antimony and uranium.

This application is a continuation-in-part of application Serial No.201,329, filed June 11, 1962, now abandoned, and of application SerialNo. 247,331, filed December 26, 1962, now US. Patent No. 3,198,750,patented August 3, 1965.

US. Patent No. 2,904,580, dated September 15, 1959, describes a catalystcomposed of antimony oxide and molybdenum oxide, as antimony molybdate,and indicates its utility in converting propylene to acrylonitrile.

British Patent 864,666, published April 6, 1961, describes a catalystcomposed of an antimony oxide alone or in combination with a molybdenumoxide, a tungsten oxide, a tellurium oxide, a copper oxide, a titaniumoxide, or a cobalt oxide. These catalysts are said to be either mixturesof these oxides or oxygen-containing compounds of antimony with theother metal; such as antimony molybdate or molybdoantimonate. Thesecatalyst systems are said to be useful in the production of unsaturatedaldehydes such as acrolein or methacrolein from olefins such aspropylene or isobutene and oxygen.

British Patent 876,446, published August 30, 1961, describes catalystsincluding antimony, oxygen and tin, and said to be either mixtures ofantimony oxides with tin oxides or oxygen-containing compounds ofantimony and tin such as tin antimonate. These catalysts are said to beuseful in the production of unsaturated aliphatic nitriles such asacrylonitrile from olefins such as propylene, oxygen and ammonia.

The catalyst In accordance with the invention, an oxidation catalyst isprovided consisting essentially of oxides of antimony and uranium. Thiscatalyst is useful not only in the oxidation of olefins to oxygenatedhydrocarbons such as unsaturated aldehydes and acids, for example,acrolein and methacrolein, and acrylic and methacrylic acid, and theoxidation of olefin-ammonia mixtures to unsaturated nitriles such asacrylonitrile, and methacrylonitrile, but also in the catalyticoxidative dehydrogenation of olefins to diolefins.

The nature of the chemical compounds which compose the catalyst of theinvention is not known. The cata lyst may be a mixture of antimony oxideor oxides and uranium oxide or oxides. It is also possible that theantimony and uranium are combined with the oxygen to form an antimonateor uranate. X-ray examination of the catalyst system has indicated thepresence of a structurally common phase of the antimony type, composedof antimony oxide, and some form of uranium oxide. Antimony tetroxidehas been identified as present. For the purposes of description of theinvention, this catalyst system will be referred to as a mixture ofantimony and uranium oxides, but this is not to be construed as meaningthat the catalyst is composed either in whole or in part of thesecompounds.

The proportions of antimony and uranium in the catalyst system may varywidely. The Sb:U atomic ratio can range from about 1:50 to about 99:1.However, optimum activity appears to be obtained at Sb:U atomic ratioswithin the range from 1:1 to 25: 1.

The catalyst can be employed without support, and will display excellentactivity. It also can be combined with an inert support, and preferablyat least 10% up to about of the supporting compound by weight of theentire composition is employed in this event. Any known supportmaterials can be used, stable under the reaction conditions to beencountered in the use of the catalyst.

The antimony oxide and uranium oxide can be blended together, or can beformed separately and then blended, or formed separately or together insitu. As starting materials for the antimony oxide component, forexample, there can be used any antimony oxide, such as antimonytrioxide, antimony tetroxide and antimony pentoxide, or mixturesthereof; or a hydrous antimony oxide, metaantimonic acid, orthoantimonicacid or pyroantimonic acid; or a hydrolyz-able or decomposable antimonysalt, such as an antimony halide, for example, antimony trichloride,trifiuoride or tribromide; antimony pentachloride and antimonypentafluoride, which is hydrolyzable in water to form the hydrous oxide.Antimony metal can be employed, the hydrous oxide being formed byoxidizing the metal with an oxidizing acid such as nitric acid.

The uranium oxide component can be provided in the form of uranium oxideor by precipitation in situ from a soluble uranium salt such as thenitrate, acetate, or a halide such as the chloride. Uranium metal can beused as a starting material, and if antimony metal is also employed, theantimony can be converted to the oxide and uranium to the nitratesimultaneously by oxidation in hot nitric acid. A slurry of hydrousantimony oxide formed in situ from the metal in nitric acid also can becombined with a solution of a uranium salt such as uranium nitrate,which is then precipitated in situ as uranium oxide by the addition ofammonium hydroxide. The ammonium nitrate and any other soluble salts areremoved by filtration of the resutling slurry.

It will be apparent from the above that uranium tribromide, uraniumtetrabrornide, uranium trichloride, uranium tetrachloride, uraniumpentachloride, uranium hexafluoride, uranium tetraiodide, uranylnitrate, uranyl sulfate, uranyl chloride, uranyl bromide, uraniumtrioxide, and uranium peroxide can be employed as the source of theuranium oxide component.

The catalytic activity of the system is enhanced by heating at anelevated temperature. Preferably, the catalyst mixture is dried andheated at a temperature of from about 500 to about 1150 F., preferablyat about 700 to 900 F., for from two to twenty-four hours. If activitythen is not suflicient, the catalyst can be further heated at atemperature above about the 1000 F. but below a temperature deleteriousto the catalyst at which it is melted or decomposed, preferably fromabout 1400 F. to about 1900 F. for from one to forty-eight hours, in thepresence of air or oxygen. Usually this limit is not reached before2000" F., and in some cases this temperature can be exceeded.

In general, the higher the activation temperature, the less timerequired to effect activation. The sufliciency of activation at anygiven set of conditions is ascertained by a spot test of a sample of thematerial for catalytic activity. Activation is best carried out in anopen chamber, permitting circulation of air or oxygen, so that anyoxygen consumed can be replaced.

The antimony oxide-uranium oxide catalyst composition of the inventioncan be defined by the following empirical formula:

Sb,U O

where a is 1 to 99, b is 50 to 1, and c is a number taken to satisfy theaverage valences of antimony and uranium in the oxidation states inwhich they exist in the catalyst as defined by the empirical formulaabove. Thus, the Sb valence may range from 3 to and the U valence fromThis catalyst system is useful in the oxidation of olefins to oxygenatedcompounds, such as aldehydes and acids, in the presence of oxygen, andin the oxidation of olefins to unsaturated nitriles in the presence ofoxygen and ammonia. Nitriles and oxygenated compounds such as aldehydesand acids can be produced simultaneously using process conditions withinthe overlapping ranges for these reactions, as set forth in detailbelow. The relative proportions of each that are obtainable will dependon the catalyst and on the olefin. The same catalyst may producepredominantly the nitrile with propylene and predominantly the aldehydeand/or acid with isobutylene. The term oxidation as used in thisspecification and claims encompasses the oxidation to aldehydes andacids and to nitriles, all of which conversions require oxygen as areactant.

Oxidation of olefins 20 nitriles The reactants used are oxygen andpropylene or isobutylene or mixtures thereof, plus ammonia.

In its preferred aspect, the process comprises contacting a mixturecomprising propylene or isobutylene, ammonia and oxygen with thecatalyst at an elevated temperature and at atmospheric or nearatmospheric pressure.

Any source of oxygen may be employed in this process. For economicreasons, however, it is preferred that air be employed as the source ofoxygen. From a purely technical viewpoint, relatively pure molecularoxygen will give equivalent results. The molar ratio of oxygen to theolefin in the feed to the reaction vessel should be in the range of0.5:1 to 4:1 and a ratio of about 1:1 to 3:1 is preferred.

Low molecular weight saturated hydrocarbons do not appear to influencethe reaction to an appreciable degree, and these materials can bepresent. Consequently, the addition of saturated hydrocarbons to thefeed to the reaction is contemplated within the scope of this invention.Likewise, diluents such as nitrogen and the oxides of carbon may bepresent in the reaction mixture without deleterious efiect.

The molar ratio of ammonia to olefin in the feed to the reaction mayvary between about 0.05:1 to 5:1. There is no real upper limit for theammonia-olefin ratio, but there is generally no reason to exceed the 5:1ratio. At ammonia-olefin ratios appreciably less than the stoichiometricratio of 1:1, various amounts of oxygenated derivatives of the olefinwill be formed.

Significant amounts of unsaturated aldehydes and even unsaturated acidsas well as nitriles will be obtained at ammonia-olefin ratiossubstantially below 1:1, i.e., in the range of 0.15:1 to 0.75:1,particularly in the case of higher olefins such as isobutylene. Outsidethe upper limit of this range only insignificant amounts of aldehydesand acids will be produced, and only very small amounts of nitriles willbe produced at ammonia-olefin ratios below the lower limit of thisrange. It is fortuitous that within the ammonia-olefin range stated,maximum utilization of ammonia is obtained, and this is highlydesirable. It is generally possible to recycle any unreacted olefin andunconverted ammonia.

A particularly surprising aspect of this invention is the eifect ofwater on the course of the reaction. We have found that in many caseswater in the mixture fed to the reaction vessel improves the selectivityof the reaction and yield of nitrile. However, reactions not includingwater in the feed are not to be excluded from this invention, inasmuchas water is formed in the course of the reaction.

In general, the molar ratio of added water to olefin, when water isadded, is at least about 0.25:1. Ratios on the order of 1:1 to 3:1 areparticularly desirable, but higher ratios may be employed, i.e., up toabout 10: 1.

The reaction is carried out at a temperature within the range of fromabout 550 to about 1100 F. The preferred temperature range is from about800 to 1000* F.

The pressure at which reaction is conducted is also an importantvariable, and the reaction should be carried out at about atmospheric orslightly above atmospheric (2 to 3 atmospheres) pressure. In general,high pressures, i.e., about 250 p.s.i.g., are not suitable, since higherpressures tend to favor the formation of undesirable by-produ-cts.

The apparent contact time is not critical, and contact times in therange of from 0.1 to about 50 seconds may be employed. The optimumcontact time will, of course, vary, depending upon the olefinbeingtreated, but in general, a contact time of from 1 to 15 seconds ispreferred.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed in the executionof this process. The process may be conducted either continuously orintermittently. The catalyst bed may be a fixed bed employing a largeparticulate or pelleted catalyst or, in the alternative, a so-calledfluidized bed of catalyst may be employed.

The reactor may be brought to the reaction temperature before or afterthe introduction of the reaction feed mixture. However, in a large scaleoperation, it is preferred to carry out the process in a continuousmanner, and in such a system the recirculation of the unreacted olefinis contemplated. Periodic regeneration or reactivation of the catalystis also contemplated, and this may be accomplished, for example, bycontacting the catalyst with air at an elevated temperature.

The products of the reaction may be recovered by any of the methodsknown to those skilled in the art. One such method involves scrubbingthe efiluent gases from the reactor with cold Water or an appropriatesolvent to remove the products of the reaction. If desired, acidifiedwater can be used to absorb the products of reaction and neutralizeunconverted ammonia. The ultimate recovery of the products may beaccomplished by conventional means. The efiiciency of the scrubbingoperation may be improved when water is employed as the scrubbing agentby adding a suitable wetting agent to the water. Where molecular oxygenis employed as the oxidizing agent in this process, the resultingproduct mixture remaining after the removal of the nitriles may betreated to remove carbon dioxide with the remainder of the mixturecontaining the unreacted olefin and oxygen being recycled through thereactor. In the case where air is employed as the oxidizing agent inlieu of molecular oxygen, the residual product after separation of thenitriles and other carbonyl products may be scrubbed with a non-polarsolvent, e.g., a hydrocarbon fraction, in order to recover unreactedolefin, and in this case the remaining gases may be discarded. Theaddition of a suitable inhibitor to prevent polymerization of theunsaturated products during the recovery steps is also contemplated.

The following examples, in the opinion of the inventors, representpreferred embodiments of the catalyst system of the invention, and ofthe processes of oxidation of olefins therewith.

Examples 1 and 2 A catalyst system composed of antimony oxide anduranium oxide, having an Sb:U atomic ratio of 8:1 was.

prepared as follows. 90 g. of antimony was dissolved in 375 cc. ofnitric acid (specific gravity 1.42) and the mixture was heated until theevolution of oxides of nitrogen had ceased. To this solution was thenadded a solution of 40.1 g. of uranyl acetate UO (C H O 2H O in 400 cc.of water. 300 cc. of ammonium hydroxide solution was then added, and thefiltered reaction slurry washed with 600 cc. of water in three 200 cc.portions. The filter cake was dried at 120 C. overnight, calcined at 800F. for 12 hours, and activated by heating at 1400 F. for 12 hours in amufile furnace open to the atmosphere.

This catalyst system was then tested for catalytic activity in theoxidation of propylene to acrylonitrile and to acrolein. A bench scaleoxidation unit of approximately 100 ml. catalyst capacity was employed.The gas feed was metered by Rotameters and water was fed by means of aSigma-motor pump through capillary copper tubing.

In the conversion to acrylonitrile, the feed molar ratio propylene/NH/air/nitrogen/water was 1/1.5/12/4/1. The apparent contact time was 5seconds. The reaction temperature was 870-880 F. The total conversionwas 79%, per pass, of which 48.6% of the propylene feed was converted toacrylonitrile and 5.3% to acetonitrile.

Examples 3 and 4 An antimony oxide-uranium oxide catalyst having an Sb:Uratio of 7:1 was prepared as follows. 45 g. of antimony metal, 150 mesh,was dissolved in 186 cc. of nitric acid (specific gravity 1.42) byboiling until the evolution of oxides of nitrogen had ceased. To thiswas added 26.7 g. of uranyl nitrate dissolved in 200 cc. of water. 150cc. of 28%. ammonium hydroxide solution was added to the mixture. Thereaction slurry was then filtered, and washed with three 100 cc.portions of wash water containing a small amount of ammonia. Thecatalyst was dried at 120 C. overnight, calcined at 800 F.

overnight and activated by heating at 1400 F. for 12 hours in a mufilefurnace open to the atmosphere.

This catalyst system was employed in the conversion of propylene toacrylonitrile using the reactor of Examples 1 and 2. Table I sets forththe reaction conditions, and the composition of the eifiuent. Inaddition to the components shown, the efiiuent contained minor amountsof carbon dioxide and hydrogen cyanide. The total coversions ofpropylene were approximately quantitative, and good conversions toacrylonitrile were obtained.

Examples 5 and 6 A silica-supported catalyst was prepared by mixing 60.6g. of the activated catalyst prepared in accordance with Examples 3 and4, with 198 g; of an aqueous silica sol containing 30.6% SiO Theresulting catalyst was dried in the oven at 120 C. with occasionalstirring for three hours, and calcined at 800 F. overnight.

The catalyst system was employed in the conversion of propylene toacrylonitrile, under the conditions and with 6 the results shown inTable H. In addition to the ingredients shown, the effluent includedminor amounts of carbon dioxide and hydrogen cyanide, and traces ofacetonitrile.

A silicon-carbide-supported catalyst was prepared by mixing 60 g. of theactivated catalyst of Examples 3 and 4 with 60 g. of silicon carbide,both through mesh. The mixture was stirred with 400 cc. of water, andthe homogeneous aqueous mixture then dried in the oven with occasionalstirring at 130 C. overnight, and calcined at 800 F. for 18 hours.

This catalyst was employed in the conversion of propylene toacrylonitrile, using a micro reactor composed of a feed inductionsystem, a molten salt bath furnace, reactor sampling valve and vaporphase chromatograph. The reactor was placed in the salt bath furnace andconnected with the feed induction system and sampling device. Thereaction was carried out at a temperature in the range of 800840 F., andthe apparent contact time was 3 seconds, using 6 g. of catalyst. Thefeed molar ratio propylene/air was 0.1. 55% of the propylene feed wasconverted to acrylontrile under these conditions.

Example 8 An antimony oxide-uranium oxide catalyst having an Sb:U ratioof 6:1 was prepared as follows. g. of antimony metal (less than 80 mesh)was heated in 372 cc. of concentrated nitric acid until the evolution ofoxides of nitrogen had ceased. To this was added 53.4 g. of uranylacetate partially dissolved in water. Water was added to dilute themixture, and then 300 ml. of 28% ammonium hydroxide was added. Theslurry was filtered, andthe filter cake washed with three 300 cc.portions of 0.1% ammonium hydroxide solution. After the last wash, airwas drawn through the filter cake for 10 minutes. The catalyst was driedat C., calcined at 800 F., and then activated by heating at 1400 F. .ina mufile furnace open to the atmosphere.

This catalyst was used in the conversion of propylene to acrylonitrile,using the micro reactor of Example 7. The catalyst charge was 5.4 g.Otherwise, the conditions were the same as Example 7. 71.8% of thepropylene feed was converted to acrylonitrile and 8.3% to acetonitrile.

Example 9 A catalyst system composed of antimony oxide and uranium oxidehaving an Sb:U ratio of 6 :1 supported on one-third of its weight ofsilica was prepared as follows. 90 g. of 80 mesh antimony was dissolvedin 360 cc. of hot concentrated nitric acid (specific gravity 1.42) andthe mixture was heated until the evolution of oxides of nitrogen hadceased, and the mixture evaporated almost to dryness. To this was thenadded 53.4 g. of uranyl acetate U02 (C2H302)2 Stirring. The mixture wasball milled for 4 hours. In removing the mass from the mill, 200 cc. ofwater was added, and then 194 g. of aqueous silica sol (30.6% SiO Withconstant stirring, 200 cc. of 28% ammonium hydroxide solution was thenadded, the slurry filtered and the precipitate washed with 300 cc. ofwater in three 100 cc. portiOns. The filter cake was dried at 120 to 130overnight, calcined at 800 F. for 20 hours, and activated by heating at1800" F. for 8 hours in a mufiie furnace open to the atmosphere.

This catalyst system was then tested for catalytic acwith 333 g. of thecatalyst. The gas feed (ammonia, isob utylene and air) was metered byRotameters, and water was fed by means of a Sigma-motor pump throughcapillary coppen tubing. The process conditions are given in Table 111.

TABLE III Percent Conversion per Pass Example Feed Ratio, iso-Temperature and Apparent No. C-4/N H3/Al1/ll20 pressure Contact Molar orvol. ratio Time, sec. Total Methacrylo- Methacrolein nitrile 10 1/1/12/4800 F., 4 p.s.i.g 4 71.9 60.0 3.

tivity in the oxidation of propylene to acrylonitrile. A bench scaleoxidation unit of approximately 100 ml. catalyst capacity was employed.The gas feed was metered by Rotameters and water was fed by means of aSigmamotor pump through capillary copper tubing.

In the conversion to acrylonitrile, the feed molar ratio propylene/NH/air/nitrogen Water was 1/1.5/12/4/4. The apparent contact time was 3seconds. The reaction temperature was 900 F. The total conversion was91% per pass, 75% of propylene feed being converted to acrylonitrile,and 1.0% to acetonitrile.

Example A catalyst system composed of antimony oxide and uranium oxidehaving a Sb:U ratio of 4.9:1 supported on one-half its Weight of silicawas prepared as follows. 75 g. of 80 mesh antimony was dissolved in 275cc. of hot concentrated nitric acid (specific gravity 1.42) and themixture was heated until the evolution of oxides of nitrogen had ceased,and the mixture evaporated almost to dryness. To this was then added53.4 g. of uranyl acetate UO (C H O 2H O with stirring. The mixture wasball milled for 4 hours. In removing the mass from the mill, 200 cc. ofwater was added, and then 226 g. of aqueous silica sol (30.6% SiO Withconstant stirring, 150 cc. of 28% ammonium hydroxide solution was thenadded, the slurry filtered, and the precipitate washed with 300 cc. ofwater in three 100 cc. portions. The filter cake was dried at 120 to 130C. overnight, calcined at 800 F. for hours, and activated by heating at1800 F. for 8 hours in a mufile furnace open to the atmosphere.

This catalyst system was then used for the oxidation of. isobuty-lene tomethacrylonitrile. A fixed bed oxidation unit was employed, in the formof a 5 foot tube of /2 inch diameter No. 40 pipe. This bed was chargedIt is apparent from Table III that the same catalyst can convertisobutylene predominantly to methacrylonitrile. Excellent per-passconversions are obtainable.

We claim:

1. A process for the oxidation of propylene and isobutylene to formacrylonitrile and methacrylonitrile, respectively, which comprises thestep of contacting in the vapor phase at a temperature within the rangefrom about 550 to about 1100 F. a mixture of ammonia, oxygen and anolefin selected from the group consisting of propylene, isobutylene, andmixtures thereof in a molar ratio of olefin to ammonia of from about1:0.05 to about 1:5, and a molar ratio of oxygen to ole-fin within therange from about 0.5:1 to about 4:1, in the presence of a catalystcomposition consisting essentially of an active catalytic oxide complexof antimony and uranium as an essential catalytic ingredient, the SbzUatomic ratio being within the range from about 1:50 to about 99:1, saidcomplex being formed by heating the mixed oxides of antimony and uraniumin the presence of oxygen at an elevated temperature of above 500 F. butbelow their melting point for a time sufiicient to form said activecatalytic oxide complex of antimony and uranium.

2. The process of claim 1, in which the SbzU atomic ratio in thecatalyst is within the range from 1:1 to 25: 1.

3. The process of claim 1, in which the catalyst composition is carriedon an inert support.

4. The process of claim 1, in which the molar ratio of oxygen to olefinis from about 1:1 to about 3:1.

5. The process of claim 1, which comprises feeding water in theolefin-ammonia-oxygen mixture in a ratio of water to olefin within therange from about 0.25:1 to about 10:1.

6. The process of claim 1, in which the reaction is carried out at apressure above atmospheric pressure up to about 250 p.s.i.g.

References Cited by the Examiner OTHER REFERENCES The Merck Index, 7thed., 1960, page 17, RS356 CHARLES B. PARKER, Primary Examiner.

JOSEPH P. BRUST, Examiner.

1. A PROCESS FOR THE OXIDATION OF PROPYLENE AND ISOBUTYLENE TO FORMACRYLONITRILE AND METHACRYLONITRILE, RESPECTIVELY, WHICH COMPRISES THESTEP OF CONTACTING IN THE VAPOR PHASE AT A TEMPERATURE WITHIN THE RANGEFROM ABOUT 550 TO ABOUT 1100*F. A MIXTURE OF AMMONIA, OXYGEN AND ANOLEFIN SELECTED FROM THE GROUP CONSISTING OF PROPYLENE, ISOBUTYLENE, ANDMIXTURES THEREOF IN A MOLAR RATIO OF OLEFIN TO AMMONIA OF FROM ABOUT1:0.05 TO ABOUT 1:5, AND A MOLAR RATIO OF OXYGEN TO OLEFIN WITHIN THERANGE FROM ABOUT 0.5:1 TO ABOUT 4:1, IN THE PRESENCE OF A CATALYSTCOMPOSITION CONSISTING ESSENTIALLY OF AN ACTIVE CATALYTIC OXIDE COMPLEXOF ANTIMONY AND URANIUM AS AN ESSENTIAL CATALYTIC INGREDIENT, THE SB:UATOMIC RATIO BEING WITHIN THE RANGE FROM ABOUT 1:50 TO ABOUT 99:1, SAIDCOMPLEX BEING FORMED BY HEATING THE MIXED OXIDES OF ANTIMONY AND URANIUMIN THE PRESENCE OF OXYGEN AT AN ELEVATED TEMPERATURE OF ABOVE 500*F. BUTBELOW THEIR MELTING POINT FOR A TIME SUFFICIENT TO FORM SAID ACTIVECATALYTIC OXIDE COMPLEX OF ANTIMONY AND URANIUM.